Fiber optic cable having a dry insert

ABSTRACT

A fiber optic cable includes at least one optical waveguide, at least one dry insert and a cable jacket. The at least one optical waveguide and at least one dry insert are at least partially disposed within a cavity of the cable jacket. In one embodiment, the cable includes a first dry insert and a second dry insert disposed within the cavity so that the at least one optical waveguide is disposed between the first dry insert and the second dry insert, thereby providing a dry cable core.

RELATED APPLICATIONS

This application is a Continuation of U.S. Ser. No. 11/606,262, filedNov. 28, 2006 now abandoned, which is a Continuation-In-Part of U.S.Ser. No. 11/351,456 filed on Feb. 10, 2006 now U.S. Pat. No. 7,277,615which is a Continuation-In-Part of U.S. Ser. No. 10/862,541 filed onJun. 7, 2004 now U.S. Pat. No. 7,177,507 which is a Continuation-In-Partof U.S. Ser. No. 10/847,807 filed on May 18, 2004 now U.S. Pat. No.7,254,302 which is a Continuation-In-Part of U.S. Ser. No. 10/661,204filed on Sep. 12, 2003 now U.S. Pat. No. 7,336,873 which is aContinuation-In-Part of U.S. Ser. No. 10/326,022 filed on Dec. 19, 2002now U.S. Pat. No. 6,970,629, all of the disclosures of which areincorporated by reference herein in their entireties.

TECHNICAL FIELD

The present application relates generally to dry packaging of opticalwaveguides. More specifically, the application relates to opticalassemblies for communication systems that include at least one dryinsert for protecting at least one optical waveguide.

BACKGROUND

Fiber optic cables include optical waveguides such as optical fibersthat transmit optical signals, for example, voice, video, and/or datainformation. One type of fiber optic cable configuration includes anoptical waveguide disposed within a tube, thereby forming a tubeassembly. Generally speaking, the tube protects the optical waveguide;however, the optical waveguide must be further protected within thetube. For instance, the optical waveguide should have some relativemovement between the optical waveguide and the tube to accommodatebending. On the other hand, the optical waveguide should be adequatelycoupled with the tube, thereby inhibiting the optical waveguide frombeing displaced within the tube when, for example, pulling forces areapplied to install the cable. Additionally, the tube assembly shouldinhibit the migration of water therein. Moreover, the tube assemblyshould be able to operate over a range of temperatures without undueoptical performance degradation.

Conventional optical tube assemblies meet these requirements by fillingthe tube with a thixotropic material such as grease. Thixotropicmaterials generally allow for adequate movement between the opticalwaveguide and the tube, cushioning, and coupling of the opticalwaveguide. Additionally, thixotropic materials are effective forblocking the migration of water within the tube. However, thethixotropic material must be cleaned from the optical waveguide beforeconnectorization of the same. Cleaning the thixotropic material from theoptical waveguide is a messy and time-consuming process. Moreover, theviscosity of thixotropic materials is generally temperature dependent.Due to changing viscosity, the thixotropic materials can drip from anend of the tube at relatively high temperatures and the thixotropicmaterials may cause optical attenuation at relatively low temperatures.

Cable designs have attempted to eliminate thixotropic materials from thetube, but the designs are generally inadequate because they do not meetall of the requirements and/or are expensive to manufacture. One examplethat eliminates the thixotropic material from the tube is U.S. Pat. No.4,909,592, which discloses a tube having conventional water-swellabletapes and/or yarns disposed therein. For instance, conventionalwater-swellable tapes are typically formed from two thin non-wovenlayers that sandwich a water-swellable powder therebetween, therebyforming a relatively thin tape that does not fill the space inside abuffer tube. Consequently, conventional water-swellable tapes do notprovide adequate coupling for the optical waveguides because of theunfilled space. Additionally, the space allows water within the tube tomigrate along the tube, rather than be contained by the conventionalwater-swellable tape. Thus, this design requires a large number ofwater-swellable components within the tube for adequately coupling theoptical fibers with the tube. Moreover, the use of large numbers ofwater-swellable components inside a buffer tube is not economicalbecause it increases the manufacturing complexity along with the cost ofthe cable.

Another example that eliminates the thixotropic material from a fiberoptic cable is U.S. Pat. No. 6,278,826, which discloses a foam having amoisture content greater than zero that is loaded with super-absorbentpolymers. The moisture content of the foam is described as improving theflame-retardant characteristics of the foam. Likewise, the foam of thisdesign is relatively expensive and increases the cost of the cable.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of a tube assembly according to anembodiment of the present invention.

FIG. 1 a is a cross-sectional view of another tube assembly according toan embodiment the present invention.

FIG. 2 is a cross-sectional view of the dry insert of the tube assemblyof FIG. 1.

FIG. 2 a-2 d are cross-sectional views of alternate dry insertsaccording to embodiments of the present invention.

FIG. 2 e is a graph depicting compression curves for three different dryinserts.

FIGS. 2 f-2 h depict various configurations of an adhesive/glueapplication to the dry insert of FIG. 2.

FIG. 3 is a bar graph depicting an optical ribbon pullout force forvarious tube configurations.

FIG. 4 is a schematic representation of a manufacturing line accordingto an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a fiber optic cable according to oneembodiment of the present invention.

FIG. 6 is a graph depicting an optical ribbon coupling force associatedwith various cable configurations.

FIG. 7 is a perspective view of another dry insert according to anembodiment of the present invention.

FIG. 8 is a cross-sectional view of another dry insert according to anembodiment of the present invention.

FIG. 9 is a perspective view of another dry insert according to the anembodiment of the present invention.

FIG. 10 is a perspective view of another dry insert according to the anembodiment of the present invention.

FIG. 11 is a cross-sectional view of a cable having a conventionalgrease filled tube assembly.

FIG. 12 is a cross-sectional view of a cable having a conventional drytube assembly.

FIG. 13 is a cross-sectional view of a fiber optic cable with an armorlayer according to an embodiment of the present invention.

FIG. 14 is a cross-sectional view of a tubeless fiber optic cableaccording to an embodiment of the present invention.

FIG. 15 is a cross-sectional view of a fiber optic cable having strandedtubes according to an embodiment of the present invention.

FIGS. 16 and 17 are cross-sectional views of a tubeless fiber opticcable according to an embodiment of the present invention.

FIGS. 18, 18 a, and 18 b are cross-sectional views of other fiber opticcables according to an embodiment of the present invention.

FIG. 18 c is a schematic representation of the cavity of the fiber opticcables depicted in FIGS. 18, 18 a, and 18 b.

FIGS. 19 and 19 a are schematic representations respectively depictingcables with zero excess ribbon length (ERL) and positive ERL.

FIGS. 19 b and 19 c are schematic representations of the cables of FIGS.19 and 19 a during bending of the same.

FIG. 20 is a cross-sectional view of a fiber optic cable having aplurality of dry inserts according to an embodiment of the presentinvention.

FIGS. 21-25 are cross-sectional views of other fiber optic cablesaccording to an embodiment of the present invention.

FIG. 26 is a schematic representation of a manufacturing line for makingthe cable of FIG. 18 according to an embodiment of the presentinvention.

FIG. 27 is a schematic representation (not to scale) of across-sectional view of an optical waveguide fiber.

FIG. 28 is a cross-sectional view of a bend-resistant optical fiber.

DETAILED DESCRIPTION

Aspects of the present invention will now be described more fullyhereinafter with reference to the accompanying drawings showingpreferred embodiments of the invention. The invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that the disclosure will fully convey the scope of theinvention to those skilled in the art. The drawings are not necessarilydrawn to scale but are configured to clearly illustrate the invention.

Illustrated in FIG. 1 is an exemplary tube assembly 10 according to oneaspect of the present invention. Tube assembly 10 includes at least oneoptical waveguide 12 such as an optical fiber, at least one dry insert14, and a tube 18. In this case, the at least one optical waveguide 12is in the form of a stack of ribbons 13 having a diagonal D dimensionacross the corners of the stack. Dry insert 14 generally surrounds theat least one optical waveguide 12 and forms core 15, which is disposedwithin tube 18. Dry insert 14 performs functions such as cushioning,coupling, inhibiting the migration of water, and accommodates bending.Dry insert 14 is advantageous because the optical waveguides are easilyremoved therefrom without leaving a residue or film that requirescleaning before connectorization. Moreover, unlike conventionalthixotropic materials, dry insert 14 does not change viscosity withtemperature variations or have a propensity to drip from an end of thetube at high temperatures. Furthermore, tube assembly 10 can includeother suitable components such as a polyester binder thread 17 to holddry insert 14 about optical waveguide 12. Likewise, two or more threadsmay be stitched together for holding dry insert 14 together beforeextruding tube 18 therearound. FIG. 1 a shows tube assembly 10′, whichis a variation of tube assembly 10. Specifically, tube assembly 10′includes a plurality of loose optical waveguides 12, instead of thestack of ribbons 13. In this case, tube assembly 10′ includestwenty-four loose optical waveguides 12 having diagonal dimension D, butany suitable number of optical waveguides may be used. Moreover, opticalwaveguides 12 may be bundled into one or more groups using binders,water-swellable threads, tapes, wraps, thin jackets, or other suitablematerials. Additionally, tube assemblies 10 or 10′ can be a portion ofcable as shown in FIG. 5. Furthermore, dry inserts 14 according to thepresent invention may be used with tubeless cable designs.

As depicted, optical waveguide 12 is an optical fiber that forms aportion of an optical fiber ribbon. In this case, the optical waveguidesare a plurality of single-mode optical fibers in a ribbon format thatform ribbon stack 13. Ribbon stack 13 can include helical or S-Zstranding. Additionally, other types or configurations of opticalwaveguides can be used. For example, optical waveguide 12 can bemulti-mode, pure-mode, erbium doped, polarization-maintaining fiber,other suitable types of optical waveguides, and/or combinations thereof.Moreover, optical waveguide 12 can be loose or in bundles. Each opticalwaveguide 12 may include a silica-based core that is operative totransmit optical signals and is surrounded by a silica-based claddinghaving a lower index of refraction than the core. Additionally, one ormore coatings can be applied to optical waveguide 12. For example, asoft primary coating surrounds the cladding, and a relatively rigidsecondary coating surrounds the primary coating. In one embodiment, oneor more optical waveguides 12 include a coating system as disclosed inU.S. patent application Ser. No. 10/632,219 filed on Jul. 18, 2003, thedisclosure of which is incorporated herein by reference. Opticalwaveguide 12 can also include an identifying means such as ink or othersuitable indicia for identification. Of course, optical waveguide canalso include a tight buffer layer. Suitable optical fibers arecommercially available from Corning Incorporated of Corning, N.Y.

In other embodiments, ribbon stack 13 can have a corner opticalwaveguide(s) 12 a with a predetermined MAC number, thereby inhibitingoptical attenuation of the corner optical waveguide when subjected tocompressive forces. Stated another way, selecting corner opticalwaveguides with a predetermined MAC number places optical waveguidesthat are less sensitive to optical attenuation from compressive forcesin ribbon stack locations that experience relatively high levels ofcompression. In other embodiments, all of the optical waveguides 12 ofthe ribbons may have a predetermined MAC number. As used herein, MACnumber is calculated as a mode field diameter (MFD) divided by a cutoffwavelength for the given optical waveguide 12 a where both quantitiesare expressed in micrometers so that the MAC number is dimensionless. Inother words, MFD is typically expressed in micrometers and cutoffwavelength is typically expressed in nanometers, so the cutoffwavelength must be divided by 1000 to convert it to micrometers, therebyyielding a dimensionless MAC number.

By way of example, the MAC number is about 7.35 or less, more preferablyabout 7.00 or less, and most preferably about 6.85 or less; however,there is a lower limit on the MAC number. By way of example, corneroptical waveguide(s) 12 a is selected with a MFD of 9.11 μm or less anda cutoff wavelength of 1240 nm or more, thereby yielding 7.35 or lessfor the MAC number. Generally speaking, the MAC number is directlyproportional to MFD and inversely proportional to the cutoff wavelength.Ribbon stack 13 has four corner optical waveguides 12 a; however, otherribbon stack configurations can include more corner positions. Forinstance, a ribbon stack having a generally plus sign shape includeseight outer corners. Likewise, other ribbon stack configurations mayhave other numbers of corner positions.

Additionally, ribbon embodiments of the present invention may have apositive excess ribbon length (ERL), although a negative ERL may bepossible with some cable designs, but generally speaking performance maybe affected. As used herein, ERL is defined as the length of theparticular ribbon minus the length of the tube or cable containing theribbon divided by the length of the tube or cable containing the ribbon,which can be expressed as a percentage by multiplying by 100. Whetherthe ERL is calculated using the tube length or the cable length dependson the particular configuration. Moreover, individual ribbons of a cablecan have different values of ERL. By way of example, ribbons of cable 50have a positive ERL, such as a positive ERL in the range of about 0.0%to about 0.4% or greater, but other suitable values may be possible.Likewise, embodiments having loose or bundled optical fibers may includea positive excess fiber length (EFL) within a suitable range for thecable configuration. Simply stated, EFL is the generic description forexcess fiber length in all configurations for optical fibers and ERLspecifically refers to the excess length of ribbons.

FIG. 2 illustrates a cross-sectional view of an explanatory dry insert14. Dry insert 14 is formed from an elongate material or materials thatare capable of being paid off from a reel for a continuous applicationduring manufacture. Dry insert 14 can be formed from a plurality oflayers that can perform different functions; however, the dry insert canbe a single layer such as a felt substance that is compressible and mayoptionally include a water-blocking/water-swellable feature. Dry insert14 cushions optical waveguide 12 from tube 18, thereby maintainingoptical attenuation of optical waveguide 12 below about 0.4 dB/km at areference wavelength of 1310 nm and 0.3 dB/km at a reference wavelengthsof 1550 nm and 1625 nm. But other suitable optical attenuation valuesare possible such as 0.35/0.25 for the respective 1310 and 1550reference wavelengths. In one embodiment, dry insert 14 is formed fromtwo distinct layers. For instance, FIG. 2 depicts a first layer 14 a ofdry insert 14 that is a compressible layer and second layer 14 b that isa water-swellable layer. In this case, first layer 14 a is formed from acompressible material having a predetermined spring constant forproviding adequate coupling characteristics. By way of example, thefirst layer is a foam tape such as an open cell foam tape; however, anysuitable compressible material can be used such as a closed cell foamtape. As shown in FIG. 2, second layer 14 b can have any suitableconstruction and in preferred embodiments is a suitable water-swellabletape having one or more components. For instance, water-swellable tapescan have different constructions as shown by the two different detailbubbles of FIG. 2, but generally include at least one tape such as anon-woven tape 14 f having a plurality of water-swellable particles 14e. However, dry insert 14 can include other types of particles formedfrom one or more materials.

First layer 14 a and second layer 14 b are preferably attached togetherwith an adhesive 14 d so that a force of about 5 Newtons (N) or more isrequired to separate the layers. Adhesive 14 d can be sprayed onto oneor both of the layers during manufacture, thereby creating a fine mistthat inhibits clusters of adhesive from forming; however, other suitableapplication methods are also possible. But, the adhesive may have otherforms such as a powder that is applied to one or more layers. Whateverthe form of adhesive used, it should not cause elevated levels ofattenuation when the dry insert is placed about the optical waveguide.Likewise, water-swellable particles or conglomerate particles such asadhesive and/or water-swellable particles should not cause microbending.In other words, the average particle size of adhesive 14 d, or otherconglomerate materials such as adhesive and water-swellable powder,should be relatively small such as 600 microns or less, preferably about450 microns or less, and most preferably about 300 microns or less sothat if the particles press against the optical waveguide through aportion of dry insert 14 they will not cause elevated levels ofmicrobending. As used herein, average particle size refers to particlesof one or more materials used in dry insert 14.

As shown in the right detail bubble of FIG. 2, second layer 14 b is awater-swellable tape having water-swellable particles 14 e disposedbetween two non-woven tape-like materials 14 f that is attached byadhesive 14 d to first layer 14 a. By way of example, adhesive 14 d maybe a dry adhesive or a heat sensitive adhesive for holding layerstogether. This construction inhibits particles from causing microbendingsince there is a non-woven tape that acts as a buffer between firstlayer 14 a and water-swellable particles 14 e. The average particle sizeof the water-swellable powder should be relatively small such as 600microns or less, preferably about 450 microns or less, and mostpreferably about 300 microns or less so that if the water-swellableparticles press against the optical waveguide through a portion of dryinsert 14 they will not cause elevated levels of microbending.Additionally, first layer 14 a (e.g., the compressible layer in thisconstruction) also acts as a buffer between the particles and opticalwaveguides. Second layer 14 b can have other constructions such as shownin the left detail bubble of FIG. 2. Specifically, this embodiment showswater-swellable particles 14 e attached to one side of a singlenon-woven tape 14 f, which is then attached to compressible first layer14 a so that water-swellable particles 14 e are disposed between thefirst and second layers without a buffer layer. In this construction,adhesive 14 f functions to attach water-swellable particles 14 e and toattach the first and second layers 14 a, 14 b of dry insert 14 together.However, this construction of dry insert 14 generally leads to a largeraverage particle size of a conglomerate material formed of adhesive andwater-swellable particles. In other words, all things being equal theaverage particle size in this dry insert construction is generallylarger because it creates a conglomerate particle compared with thewater-swellable particle alone. Consequently, this may cause elevatedmicrobending if the average particle size becomes too large. So in thisconstruction the average particle size of the conglomerate or compositeparticle should be in the same range as stated above for inhibitingmicrobending.

Likewise, the inner surface of dry insert 14 should not cause elevatedlevels of microbending. Thus, in preferred embodiments, a surface of thelayer that can contact the optical waveguides should have a relativelysmooth surface and a suitable compressibility or softness for preservingsuitable levels of optical performance. For instance, if foam is used asfirst layer 14 a of dry insert 14 an average cell size of the foam isabout 1000 microns or less, and can be about 700 microns or less,thereby creating a relatively smooth surface. Additionally, the foam mayhave layers with different size cells such as larger cells away from theoptical waveguides and smaller cells near the surface of the foam thatcan contact the optical waveguides. Other variations include a surfacetreatment for smoothing the surface of the foam layer. Surfacetreatments include heating to smooth out the surface or filling thecells with a suitable material. Additionally, first layer 14 a such asfoam cushions the water-swellable particles and/or adhesive of dryinsert 14 from causing microbending.

In one embodiment, the first layer is an open cell polyurethane (PU)foam tape. The PU foam tape may either be an ether-based PU or anester-based PU, but other suitable foam tape compressible layers can beused such as a polyethylene foam, a polypropylene foam, or EVA foam.However, preferred embodiments use an ether-based foam tape since itperforms better than an ester-based PU foam when subject to moisture. Inother words, the ester-based PU foam can break down with moisture,whereas the ether-based PU foam is generally more robust with respect tomoisture. Additionally, the foam layer has a predetermined densitygenerally in the range of about 1 lb/ft³ to about 3 lb/ft³, but inpreferred embodiments the density is about 2 lb/ft³. Dry insert 14 alsohas a predetermined ultimate tensile strength to inhibit breakage duringmanufacture. Generally speaking, with dry inserts having both acompressible layer and a water-swellable layer the majority of thetensile strength is provided by the water-swellable layer(s). Theultimate tensile strength of the dry insert is about 10 Newtons percentimeter or greater per centimeter width W of dry insert 14,preferably about 20 Newtons per centimeter width W of dry insert 14 orgreater.

Still further, dry inserts of the present invention can use othersuitable materials and/or constructions while still providingcushioning, coupling, and/or allowing movement of the optical fibers.Moreover, like the other dry inserts the water-swellable layer isoptional and can use any suitable material(s)/construction(s). FIG. 2 adepicts one example of another dry insert 14′. Dry insert 14′ includes acompressible layer formed from a plurality of microspheres 14 b′disposed between a top tape 14 a′ and bottom tape 14 a′. As with othertapes, tapes 14 a′ can be formed from any suitable material such as anon-woven material, Mylar, or other like materials. More specifically,microspheres 14 b′ are generally disposed between tapes 14 a′ and areattached using a suitable method such as an adhesive, bonding agent,application of heat and/or pressure, or the like. Additionally, anoptional water-swellable substance such as a plurality ofwater-swellable particles or water-swellable coating 14 c′ may also bedisposed between tapes 14 a′ with microspheres 14 b′ or on a portion oneor more tapes 14 a′. Suitable materials for microspheres 14 b′ arerelatively soft so they are compressible and sized so that they will notcause undue levels of optical attenuation if they press against theoptical fiber or ribbon. By way of example, suitable hollow microspheresare available from Akzo Nobel of the Netherlands under the tradenameEXPANCEL and includes copolymers of monomers vinylidine chloride,acrylonitrile, and methylmethacrylate. Other plastic hollow microspheresare available from Asia Pacific Microspheres of Malaysia under thetradename of PHENOSET, which are phenolic and amino-based microspheres.

The compressible nature of hollow polymeric microspheres is suited forproviding adequate coupling of the optical fibers to the tube or cablejacket. Additionally, the smooth generally round surface of thesemicrospheres permits pressing against the optical fibers withoutinducing elevated levels of optical attenuation such as during bending,twisting, or crushing of the cable. Additionally, the size of the hollowmicrospheres can vary from about 1 micron to about 300 microns,likewise, a wall thickness of the microspheres can also vary from about0.1 micron up to several microns, but other suitable dimensions arepossible as long as a suitable level of optical performance ismaintained.

FIG. 2 b depicts another example of a dry insert 14″ that provides acompressible layer 14 b″ using geometry of its shape. More specifically,compressible layer 14 b″ is provided by using a dimensional fabric thathas a generally textured shape in one or more directions for providingthe compressible layer. As shown, dry insert 14″ has a generallytextured shape TS and is formed from a suitably soft and flexiblematerial so that it can deform for providing an adequate level ofcoupling for the optical fibers or ribbons without causing undue levelsof optical attenuation. By way of example, suitable fabrics areavailable from Freudenberg of Durham, N.C. under the name of Novolon.The dimensional fabrics may be formed from a variety of materials suchas polyester, polypropylene, nylon, or other suitable materials.Generally speaking, dimensional fabrics are formed using a moldingprocess for transforming a two-dimensional (i.e., flat) fabric orsubstrate into a three-dimensional (i.e., textured shape) fabric orsubstrate with the desired textured shape TS. The coupling and/orcompressibility of dry insert 14″ can be tailored by changing parameterssuch as the number of contact points per surface area (i.e., changingthe density of high and low contact points), the height from a highpoint to a low point, the dimension fabric profile, and/or flexibilityof the dimensional fabric. Again, dry insert 14″ can include an optionalwater-swellable layer 14 a″ for blocking the migration of water alongthe cable or tube assembly. For instance, the water-swellable layer maybe a coating applied to one or more surfaces or applied to the fibers ofthe dimensional fabric, include water-swellable particles disposed in oron the dry insert, and/or may include superabsorbent fibers. Suitablewater-swellable filaments are, for example, LANSEAL materials availablefrom Toyobo of Osaka, Japan or OASIS materials available from TechnicalAbsorbents Ltd. of South Humberside, United Kingdom.

FIG. 2 c depicts a further embodiment of a dry insert 14″′ having acompressible layer 14 b″′ having a non-woven layer of felt substancemade of one or more materials formed from non-continuous and/orcontinuous filaments. Dry insert 14″′ may optionally include awater-swellable layer and/or one or more tapes for attaching the feltsubstance thereto. For instance, dry insert 14″′ includes a plurality ofwater-swellable filaments 14 a″′ along with other filaments 14 b″′ thatare non-swellable disposed between a plurality of optional tapes 14 c″′,thereby forming dry insert 14″′, As used herein, “felt substance” meansa material comprising one or more types of non-continuous or continuousfilaments and/or fibers which have been caused to adhere and/or matttogether through the action of heat, moisture, chemicals, pressure, ormechanical action such as needle-punching or spun-lacing, or acombination of the foregoing actions, thereby forming a relatively thickand compressible layer. Water-swellable filaments 14 a″′ may compriseany suitable water-swellable material. By way of example, dry insert14″′ of FIG. C may include about 25% or less by weight ofwater-swellable filaments 14 a″′ and about 75% or more by weight ofother filaments 14 b″′; however, other suitable ratios are possible.Other filaments 14 b″′ may include any suitable filament and/or fibermaterial such as polymer filaments like polypropylene, polyethylene, andpolyesters, likewise, other suitable materials such as cottons, nylon,rayons, elastomers, fiberglass, aramids, polymers, rubber-basedurethanes, composite materials and/or blends thereof may be included asa portion of other filaments 14 b″′ and may be tailored for providingspecific characteristics.

FIG. 2 d depicts yet another dry insert 14″″ shaped as a generally flattape having a compressible layer with a suitable width. By way ofexample, dry insert 14″″ is made of a plurality of filaments 14 c″″ suchas a plurality of generally continuous polyester filaments groupedtogether by a compressible layer 14 b″″ that acts as a matrix material,but the use of other filament materials is possible. Compressible layer14 b″″ is formed by, for instance, foaming the matrix material, therebyproviding a compressible layer 14 b″″. Additionally the matrix materialis used for attaching a plurality of water-swellable particles to dryinsert 14″″ for forming a water-swellable layer 14 a″″. Suitable foamedmatrix materials include vinyls, polyurethanes, polypropylenes, EVAs, orpolyethylene blends. The plurality of filaments and the matrix materialare run through a die that forms dry insert 14″″ into its desired shapesuch as a generally flat ribbon-like profile. Dry inserts 14″′ may berun parallel to the fiber ribbons in a sandwich configuration or haveother configurations such as helically wrapped about the optical fibersor ribbon stack. Other similar constructions are possible using anysuitable materials for providing the compressible layer and thewater-swellable layer. Dry insert can include still other constructionsand/or materials such as sponge-like materials for a compressible layersuch as polyvinylalcohol (PVA).

Dry insert 14 may have a water-swell speed so that the majority of swellheight of the water-swellable substance occurs within about 120 secondsor less of being exposed to water, more preferably about 90 seconds orless. By way of example, dry insert 14 may have a maximum swell heightof about 18 mm for distilled water and about 8 mm for a 5% ionic watersolution i.e., salt water in a unrestricted swell state; however, dryinserts with other suitable maximum swell heights may be used. Tubeassemblies may be constructed with a water-swell ratio of about 3 ormore, about 5 or more, and up to about 7 or more. Water-swell ratio isdefined as the unrestricted cross-sectional swell state area of the dryinsert divided by the free space in the tube assembly. For round cables,the free space of the tube assembly is defined as an area of an innerdiameter of the tube minus the area that the optical waveguides occupy.For instance, if the dry insert has an unrestricted cross-sectionalswell state area of 50 mm² and the tube has a free space of 10 mm² thewater-swell ratio is five. Dry inserts can also include pre-treatmentsfor improving performance such as wetting agent that decreases thesurface tension of a portion of the dry insert. For instance, ahydrophilic substance is sprayed onto the dry insert so that liquid caneasily and quickly move through the dry insert so the liquid caninteract with the water-swellable layer. Additionally, dry inserts caninclude the selection of hydrophilic components such as hydrophilicfoams for use within the same.

Dry insert 14 may be compressed during assembly so that it provides apredetermined normal force that inhibits optical waveguide 12 from beingeasily displaced longitudinally along tube 18. Dry inserts 14 preferablyhave an uncompressed height h of about 5 mm or less for minimizing cablesize such as the tube diameter and/or cable diameter of a round cable;however, any suitable height h can be used for dry insert 14.Additionally, height h of dry insert 14 need not be constant across thewidth, but can vary, thereby conforming to the cross-sectional shape ofthe optical waveguides and providing improved cushioning to improveoptical performance (FIG. 10). Second layer 14 b is a water-swellablelayer such as a tape that inhibits the migration of water within tube18.

Compression of dry insert 14 is actually a localized maximum compressionof dry insert 14. In the case of FIG. 1, the localized maximumcompression of dry insert 14 occurs at the corners of the ribbon stackacross the diameter. In other cable designs such as depicted in FIG. 18,the localized maximum compression of the dry insert generally occurs atthe maximum amplitude of undulating ribbon stack as will be discussed.Calculating the percentage of compression of dry insert 14 in FIG. 1requires knowing an inner diameter of tube 18, a diagonal D dimension ofthe ribbon stack, and an uncompressed height h of dry insert 14. By wayof example, inner diameter of tube 18 is 7.1 mm, diagonal D of theribbon stack is 5.1 mm, and the uncompressed height h of dry insert 14across a diameter is 3.0 mm (2 times 1.5 mm). Adding diagonal D (5.1 mm)and the uncompressed height h of dry insert 14 across the diameter (3.0mm) yields an uncompressed dimension of 8.1 mm. When placing the ribbonstack and dry insert 14 and into tube 18 with an inner diameter of 7.1mm, dry insert is compressed a total of 1 mm (8.1 mm−7.1 mm). Thus, dryinsert 14 is compressed by about thirty percent across the diameter oftube 18.

FIG. 2 a is a graph depicting exemplary compression curves 200, 202, and204 for three different dry inserts 14. Specifically, curves 200 and 202represent two different dry inserts each having a compressible open cellether-based PU foam layer and a water-swellable layer. Curves 200 and202 respectively represent dry inserts with respective heights h ofabout 1.5 mm and about 1.8 mm. On the other hand, curve 204 represents adry insert having a compressible open cell ester-based PU foam layer anda water-swellable layer with a height of about 1.8 mm. The compressioncurves were generated by placing the dry insert sample between twocircular plates having a diameter of about 2.2 inches while measuringthe force required to compress the sample using an Instron machine.

As shown, the compression curves for all three dry inserts 14 aregenerally non-linear over the compression range. But generally speaking,compression curves 200, 202, and 204 have a generally linear compressionup to about 0.70 mm. In one embodiment, dry insert 14 has compression ofabout 1.0 mm or less with a force of about 10 Newtons. Generallyspeaking, the foam layer is being compressed while the water-swellablelayer is relatively uncompressible.

In other embodiments, first layer 14 a of dry insert 14 is uncompressedin tube assembly 10, but begins to compress if optical waveguidemovement is initiated. Other variations include attaching or bonding aportion of dry insert 14 to tube 18. For example, adhesives, glues,elastomers, and/or polymers 14 c are disposed on a portion of thesurface of dry insert 14 that contacts tube 18 for attaching dry insert14 to tube 18. For instance, layer 14 c is a polymer layer that at leastpartially melts during the extrusion of tube 18, thereby creating a bondtherebetween. Likewise, dry inserts can include other suitable materialsand/or layers for other purposes such as a flame-retardant materialand/or layer. Additionally, it is possible to helically wrap dry insert14 about optical waveguide 12, instead of being longitudinally disposed.In still further embodiments, two or more dry inserts can be formedabout one or more optical waveguides 12 such as two halves placed withintube 18.

Other embodiments may include a fugitive glue/adhesive is used forcoupling cable core 15 and/or dry insert 14 with tube 18. Theglue/adhesive or the like is applied to the radially outward surface ofdry insert 14, for instance, during the manufacturing process. Thefugitive glue/adhesive is applied while hot or melted to the outersurface of dry insert 14 and then is cooled or frozen when the cable isquenched or cools off. By way of example, a suitable fugitive glue isavailable from National Starch and Chemical Company of Bridgewater, N.J.under the tradename LITE-LOK® 70-003A. The fugitive glue or othersuitable adhesive/material may be applied in beads having a continuousor an intermittent configuration as shown in FIGS. 2 b-2 d. Forinstance, one or more adhesive/glue beads may be longitudinally appliedalong the dry insert, longitudinally spaced apart beads, in a zig-zagbead along the longitudinal axis of the dry insert, or in any othersuitable configuration.

In one application, a plurality of beads of fugitive glue/adhesive orthe like is applied to dry insert 14. For instance, three continuous, ornon-continuous, beads can be disposed at locations so that when the dryinsert is formed about the ribbon stack the beads are about 120 degreesapart. Likewise, four beads can be disposed at locations so they areabout 90 degrees apart when the dry insert is formed about the opticalwaveguides. In embodiments having the beads spaced apart along thelongitudinal axis, the beads may have a longitudinal spacing S of about20 mm and about 800 mm or more; however, other suitable spacing may beused. Additionally, beads may be intermittently applied for minimizingthe amount of material required, thereby reducing manufacturing expensewhile still providing sufficient coupling/adhesion.

Since tube assemblies 10 are not filled with a thixotropic material thetube may deform or collapse, thereby forming an oval shaped tube insteadof a round tube. U.S. patent application Ser. No. 10/448,509 filed onMay 30, 2003, the disclosure of which is incorporated herein byreference, discusses dry tube assemblies where the tube is formed from abimodal polymeric material having a predetermined average ovality. Asused herein, ovality is the difference between a major diameter D1 and aminor diameter D2 of tube 18 divided by major diameter D1 and multipliedby a factor of one-hundred, thereby expressing ovality as a percentage.Bimodal polymeric materials include materials having at least a firstpolymer material having a relatively high molecular weight and a secondpolymer material having a relatively low molecular weight that aremanufactured in a dual reactor process. This dual reactor processprovides the desired material properties and should not be confused withsimple post reactor polymer blends that compromise the properties ofboth resins in the blend. In one embodiment, the tube has an averageovality of about 10 percent or less. By way of example, tube 18 isformed from a HDPE available from the Dow Chemical Company of Midland,Mich., under the tradename DGDA-2490 NT.

FIG. 3 is a bar graph depicting a normalized optical ribbon pulloutforce (N/m) for various tube and/or cable configurations. The ribbonpullout force test measured the force required to initiate movement of aribbon stack along its entire length from a 10-meter length of cable. Ofcourse, this pullout force test is equally applicable to loose orbundled optical waveguides. Specifically, the stack of ribbons waspulled from the tube and the force required to initiate movement of theentire length of ribbons was divided by the length of the cable, therebynormalizing the optical ribbon pullout force. As a baseline forcomparison, bar 30 depicts a ribbon pullout force of about 4.8 N/m for aribbon stack of 120-fibers in conventional grease (a thixotropicmaterial) filled tube (FIG. 11). Bar 31 depicts a ribbon pullout forcefor a conventional dry tube design solely having a water-sweflable tapearound a ribbon stack of 144-fibers (similar to FIG. 12), which areloosely disposed in a tube. Specifically, bar 31 depicts a ribbonpullout force of about 0.6 N/m for the 144-fiber ribbon stack. Thus, theconventional dry tube design (FIG. 12) has a ribbon pullout force thatis about twelve percent of the ribbon pullout force of the conventionalgrease filled tube (FIG. 11), which is inadequate for proper cableperformance.

Bars 32, 34, 36, and 38 represent tube assemblies according to thepresent invention and bar 39 represents cable 180 depicted in FIG. 18.Specifically, bar 32 depicts a ribbon pullout force of a 144-fiber stackfrom a tube assembly 10 having dry insert 14 with an uncompressed heighth of about 1.5 mm with about a zero percent compression of dry insert14. In this embodiment, bar 32 depicts a ribbon pullout force of about1.0 N/m, which is a surprising improvement over the conventional drytube. Bars 34 and 36 represent configurations where dry insert 14 iscompressed within tube assembly 10 by a percentage from its originalheight to an average compressed height. More specifically, bar 34represents a ribbon pullout force of a similar tube assembly as bar 32,expect that in this embodiment dry insert 14 is compressed about thirtypercent. In this embodiment, bar 34 depicts a ribbon pullout force ofabout 2.7 N/m. Bar 36 represents a ribbon pullout force of a 144-fiberribbon stack from a tube assembly with dry insert 14 having anuncompressed height h of about 3 mm, which is compressed by about thirtypercent within the tube. In this embodiment, bar 36 depicts a ribbonpullout force of about 0.5 N/m. Bar 38 represents a ribbon pullout forceof a 144-fiber stack from a tube assembly 10 having dry insert 14 withan uncompressed height h of about 1.5 mm with about a seventeen percentcompression of dry insert 14 and glue beads. In this case, four gluebeads were continuously applied longitudinally along the dry insert sothat they were spaced at about 90 degrees. The ribbon pullout force forthis embodiment was about 4.0 N/m. As shown, the application ofadhesive/glue beads increased the ribbon pullout force with lesscompression of the dry insert. Thus, according to the concepts of thepresent invention the compression of dry insert 14 may be in the rangeof about 10% to about 90%; however, other suitable ranges of compressionor even no compression may provide the desired performance depending onthe configuration. Nonetheless, the compression of dry insert 14 shouldnot be so great as to cause undue optical attenuation in any of theoptical waveguides and can be increased with the use of adhesive/gluebeads. Bar 39 depicts a ribbon pullout force of about 1.5 N/m for a 96fiber four ribbon stack from a cable jacket 188 of cable 180 asdiscussed in more detail below. Preferably, the ribbon pullout force, orpullout force for other optical waveguide configurations, is in therange of about 0.5 N/m and about 5.0 N/m, more preferably, in the rangeof about 1 N/m to about 4 N/m.

FIG. 4 schematically illustrates an exemplary manufacturing line 40 fortube assembly 10 according to the present invention; however, othervariations of the concepts may be used to manufacture other assembliesand/or cables according to the concepts of the present invention.Manufacturing line 40 includes at least one optical waveguide payoffreel 41, a dry insert payoff reel 42, an optional compression station43, an glue/adhesive station 43 a, a binding station 44, a cross-headextruder 45, a water trough 46, and a take-up reel 49. Additionally,tube assembly 10 may have a sheath 20 therearound, thereby forming acable 50 as illustrated in FIG. 5. Sheath 20 can include strengthmembers 19 a and a jacket 19 b, which can be manufactured on the sameline as tube assembly 10 or on a second manufacturing line. Theexemplary manufacturing process includes paying-off at least one opticalwaveguide 12 and dry insert 14 from respective reels 41 and 42. Only onepayoff reel for optical waveguide 12 and dry insert 14 are shown forclarity; however, the manufacturing line can include any suitable numberof payoff reels to manufacture tube assemblies and cables according tothe present invention. Next, dry insert 14 is compressed to apredetermined height h at compression station 43 and an optionaladhesive/glue is applied to the outer surface of dry insert 14 atstation 43 a. Then dry insert 14 is generally positioned about opticalwaveguide 12 and if desired binding station wraps or sews one or morebinding threads around dry insert 14, thereby forming core 15.Thereafter, core 15 is feed into cross-head extruder 45 where tube 18 isextruded about core 15, thereby forming tube assembly 10. Tube 18 isthen quenched in water trough 46 and then tube assembly 10 is wound ontotake-up reel 49. As depicted in the box, if one manufacturing line isset-up to make cable 50, then strength members 19 a are paid-off reel 47and positioned adjacent to tube 18, and jacket 19 b is extruded aboutstrength members 19 a and tube 18 using cross-head extruder 48.Thereafter, cable 50 passes into a second water trough 46 before beingwound-up on take-up reel 49. Additionally, other cables and/ormanufacturing lines according to the concepts of the present inventionare possible. For instance, cables and/or manufacturing lines mayinclude a water-swellable tape 19 c and/or an armor between tube 18 andstrength members 19 a; however, the use of other suitable cablecomponents are possible.

FIG. 6 is a graph depicting the results of a ribbon coupling force forcables having the similar tube assemblies as used in FIG. 3. The ribboncoupling force test is used for modeling the forces applied to theoptical waveguide(s) when subjecting a cable to, for example, pullingduring installation of the cable. Although the results between theribbon pullout force and the ribbon coupling force may have forces inthe same general range, the ribbon coupling force is generally a betterindicator of actual cable performance.

In this case, the ribbon coupling test simulates an underground cableinstallation in a duct by applying 600 pounds of tension on a 250 mlength of cable by placing pulling sheaves on the respective sheathes ofthe cable ends. However, other suitable loads, lengths, and/orinstallation configurations can be used for characterizing ribboncoupling in other simulations. Then, the force on the opticalwaveguide(s) along its length is measured from the end of cable. Theforce on the optical waveguide(s) is measured using a Brillouin OpticalTime-Domain Reflectometer (BOTDR). Determining a best-fit slope of thecurve normalizes the ribbon coupling force.

As a baseline for comparison, curve 60 depicts a normalized ribboncoupling force of about 1.75 N/m for a cable having a ribbon stack of120-fibers in conventional grease filled cable (FIG. 11). Curve 62depicts a ribbon pullout force for a cable having a conventional drytube design having a water-swellable tape around a ribbon stack of144-fibers (FIG. 12), which are loosely disposed in a tube.Specifically, curve 62 depicts a normalized ribbon coupling force ofabout 0.15 N/m for the 144-fiber ribbon stack. Thus, the conventionaldry tube design (FIG. 12) has a normalized ribbon coupling force that isabout nine percent of the normalized ribbon coupling force of theconventional grease filled tube (FIG. 11), which is inadequate forproper cable performance. In other words, the ribbon stack of theconventional dry tube cable is easily displacable during stretching ofthe cable sheath, for example, during aerial ice loading, aerialgalloping, cable dig-ups, and pulling during installation of the cable.

Curves 64, 66, 68, and 69 represent cables according to the presentinvention. Specifically, curve 64 depicts a ribbon coupling force of acable having a 144-fiber stack with a tube assembly 10 having dry insert14 with an uncompressed height h of about 1.5 mm with about a zeropercent compression of dry insert 14. In this embodiment, curve 64depicts a ribbon coupling force of about 0.80 N/m, which is animprovement over the conventional dry cable of FIG. 12. Curves 66 and 68represent cable configurations where dry insert 14 is compressed withintube assembly 10 by a percentage from its original height to an averagecompressed height. More specifically, curve 66 represents a ribboncoupling force of a similar cable as curve 64, expect that in thisembodiment dry insert 14 is compressed about thirty percent. In thisembodiment, curve 66 depicts a ribbon coupling force of about 2.80 N/m.Curve 68 represents a ribbon coupling force of a cable having a144-fiber ribbon stack from a cable having a tube assembly with dryinsert 14 having an uncompressed height h of about 3 mm, which iscompressed by about thirty percent within the tube. In this embodiment,curve 68 depicts a ribbon coupling force of about 0.75 N/m. Curve 69represents a ribbon coupling force of a cable having a 144-fiber ribbonstack from a cable having a tube assembly with dry insert 14 having anuncompressed height h of about 1.5 mm, which is compressed by aboutseventeen percent within the tube and includes adhesive/glue beads. Inthis case, four glue beads were continuously applied longitudinallyalong the dry insert so that they were spaced at about 90 degrees. Asshown, curve 69 depicts a ribbon coupling force that is similar to curve66, about 2.80 N/m, with less compression of the dry insert. Thus,according to the concepts of the present invention the ribbon couplingforce is preferably in the range of about 0.5 N/m to about 5.0 N/m, morepreferably, in the range of about 1 N/m to about 4 N/m. However, othersuitable ranges of ribbon coupling force may provide the desiredperformance.

Additionally, the concepts of the present invention can be employed withother configurations of the dry insert. As depicted in FIG. 7, dryinsert 74 has a first layer 74 a and a second layer 74 b that includesdifferent suitable types of water-swellable substances. In oneembodiment, two different water-swellable substances are disposed in, oron, second layer 14 b so that tube assembly 10 is useful for multipleenvironments and/or has improved water-blocking performance. Forinstance, second layer 14 b can include a first water-sweflablecomponent 76 effective for ionized liquids such as saltwater and asecond water-swellable component 78 effective for non-ionized liquids.By way of example, first water-swellable material is apolyacrylamide-acrylate copolymer and second water-swellable material isa polyacrylate superabsorbent. Moreover, first and secondwater-swellable components 76,78 can occupy predetermined sections ofthe water-swellable tape. By alternating the water-swellable materials,the tape is useful for standard applications, salt-water applications,or both. Other variations of different water-swellable substancesinclude having a water-swellable substance with different swell speeds,gel strengths and/or adhesion with the tape.

FIG. 8 depicts another embodiment of the dry insert. Dry insert 84 isformed from three layers. Layers 84 a and 84 c are water-swellablelayers that sandwich a layer 84 b that is compressible for providing acoupling force to the at least one optical waveguide. Likewise, otherembodiments of the dry insert can include other variations such at leasttwo compressible layers sandwiching a water-swellable layer. The twocompressible layers can have different spring constants for tailoringthe normal force applied to the at least optical waveguide.

FIG. 9 illustrates a dry insert 94 having layers 94 a and 94 b accordingto another embodiment of the present invention. Layer 94 a is formedfrom a closed-cell foam having at least one perforation 95 therethroughand layer 94 b includes at least one water-sweflable substance; however,other suitable materials can be used for the compressible layer. Theclosed-cell foam acts as a passive water-blocking material that inhibitswater from migrating therealong and perforation 95 allows an activatedwater-swellable substance of layer 94 b to migrate radially inwardtowards the optical waveguide. Any suitable size, shape, and/or patternof perforation 95 that allows the activated water-swellable substance tomigrate radially inward to effectively block water is permissible. Thesize, shape, and/or pattern of perforations can be selected and arrangedabout the corner optical waveguides of the stack, thereby improvingcorner optical waveguide performance. For example, perforations 95 canprovide variation in dry insert compressibility, thereby tailoring thenormal force on the optical waveguides for maintaining opticalperformance.

FIG. 10 depicts dry insert 104, which illustrates other concepts of thepresent invention. Dry insert 104 includes layers 104 a and 104 b. Layer104 a is formed of a plurality of non-continuous compressible elementsthat are disposed on layer 104 b, which is a continuous water-swellablelayer. In one embodiment, the elements of layer 104 a are disposed atregular intervals that generally correlate with the lay length of aribbon stack. Additionally, the elements have a height h that variesacross their width w. Stated another way, the elements are shaped toconform to the shape of the optical waveguides they are intended togenerally surround.

FIG. 13 depicts cable 130, which is another embodiment of the presentinvention that employs tube assembly 10. Cable 130 includes a sheathsystem 137 about tube assembly 10 for protecting tube assembly 10 from,for instance, crushing forces and environmental effects. In this case,sheath system 137 includes a water-swellable tape 132 that is secured bya binder thread (not visible), a pair of ripcords 135, an armor tape136, and a jacket 138. Armor tape 136 is preferably rolled formed;however, other suitable manufacturing methods may be used. The pair ofripcords 135 are generally disposed about one-hundred and eighty degreesapart with about ninety degree intervals from the armor overlap, therebyinhibiting the shearing of ripcord on an edge of the armor tape duringuse. In preferred embodiments, ripcords suitable for ripping through anarmor tape have a construction as disclosed in U.S. patent applicationSer. No. 10/652,046 filed on Aug. 29, 2003, the disclosure of which isincorporated herein by reference. Armor tape 136 can be either adielectric or a metallic material. If a dielectric armor tape is usedthe cable may also include a metallic wire for locating the cable inburied applications. In other words, the metallic wire makes the cabletonable. Jacket 138 generally surrounds armor tape 136 and providesenvironmental protection to cable 130. Of course, other suitable sheathsystems may be used about the tube assembly.

FIG. 14 depicts fiber optic cable 140. Cable 140 includes at least oneoptical waveguide 12 and a dry insert 14 forming a cable core 141 withina sheath system 142. In other words, cable 140 is a tubeless designsince access to the cable core 141 is accomplished by solely cuttingopen sheath system 142. Sheath system 142 also includes strength members142 a embedded therein and disposed at about 180 degrees apart, therebyimparting a preferential bend to the cable. Of course, other sheathsystems configurations such as different types, quantities, and/orplacement of strength members 142 a are possible. Cable 140 may alsoinclude one or more ripcords 145 disposed between cable core 141 andsheath 142 for ripping sheath 142, thereby allowing the craftsman easyaccess to cable core 141.

FIG. 15 depicts a fiber optic cable 150 having a plurality of tubeassemblies 10 stranded about a central member 151. Specifically, tubeassemblies 10 along with a plurality of filler rods 153 are S-Z strandedabout central member 151 and are secured with one or more binder threads(not visible), thereby forming a stranded cable core. The stranded cablecore has a water-swellable tape 156 thereabout, which is secured with abinder thread (not visible) before jacket 158 is extruded thereover.Optionally, aramid fibers, other suitable strength members and/or waterblocking components such as water-swellable yarns may be stranded aboutcentral member 151, thereby forming a portion of the stranded cablecore. Likewise, water-swellable components such as a yarns or tape maybe placed around central member 151 for inhibiting water migration alongthe middle of cable 150. Other variations of cable 150 can include anarmor tape, an inner jacket, and/or different numbers of tubeassemblies.

FIGS. 16 and 17 depict explanatory tubeless cable designs according tothe present invention. Specifically, cable 160 is a drop cable having atleast one optical waveguide 12 generally surrounded by dry insert 14within a cavity of jacket 168. Cable 160 also includes at least onestrength member 164. Other tubeless drop cable configurations are alsopossible such as round or oval configurations. FIG. 17 depicts atubeless figure-eight drop cable 170 having a messenger section 172 anda carrier section 174 connected by a common jacket 178. Messengersection 172 includes a strength member 173 and carrier section 174includes a cavity having at least one optical waveguide 12 that isgenerally surrounded by dry insert 14. Carrier section 174 can alsoinclude at least one anti-buckling member 175 therein for inhibitingshrinkage when carrier section 174 is separated from messenger section172. Although, FIGS. 16 and 17 depict the dry insert of FIG. 2 anysuitable dry insert may be used.

FIGS. 18, 18 a, and 18 b respectively depict cables 180, 180′, and 180″that employ the concepts of the present invention in a tubeless cableconfiguration having a generally flat shape. Cable 180 includes at leastone optical waveguide 12 and a plurality of dry inserts 184 a, 184 bthat are at least partially disposed within a cavity 188 a of a cablejacket 188. As depicted, the major (e.g. planar) surfaces (not numbered)of dry inserts 184 a, 184 b are generally aligned with major (e.g.horizontal) surfaces (not numbered) of cavity 188 a, thereby allowing acompact and efficient configuration while generally inhibiting cornerfiber contact as occurs with a ribbon stack in a round tube. In thisembodiment, optical waveguide 12 is a portion of an optical fiber ribbon182 (represented by the horizontal line) and dry inserts 184 a, 184 bsandwich a plurality of ribbons 182 in a non-stranded stack, therebyforming a cable core 185. Consequently, cable 180 has the ribbon(s) 182,major surfaces of the dry inserts 184 a, 184 b, and major surfaces ofcavity 188 a generally aligned or generally parallel. Additionally, dryinserts 184 a, 184 b contact at least a portion of respective top orbottom ribbons 182. Cable 180 further includes at least one strengthmember 189 for providing tensile strength and in this embodimentincludes two strength members 189 disposed on opposite sides of cavity188 a. Strength members 189 may be formed from any suitable materialssuch as dielectrics, conductors, composites or the like. Cable 180 andsimilar cables are advantageous as a distribution cable as disclosed inU.S. patent application Ser. No. 11/193,516 filed on Jul. 29, 2005, thedisclosure of which is incorporated herein by reference. Cable 180′ issimilar to cable 180, but has six loose optical fibers 12 (instead ofribbons) disposed between dry inserts 184 a and 184 b. Again, opticalfibers 12 contact at least a portion of one of the dry inserts 184 a,184 b. Of course, cables 180,180′, 180″ and other similar cables mayhave applications besides distribution cables such as long-haul, campus,drop, indoor, or other applications.

Although, cable 180 depicts four optical fiber ribbons 182 in the ribbonstack, other embodiments of the present invention can include more thanfour optical fiber ribbons in the ribbon stack. However, designs withmore than four optical fiber ribbons may require the use of bendresistant optical fibers for accommodating the higher ERL level that,generally speaking, is required as the number of optical fiber ribbonsin the non-stranded stack increases, thereby maintaining suitableoptical performance during bending and the like. Besides more ribbons inthe stack, the use of bend resistant optical fibers in fiber optic cabledesigns may allow a smaller bend radius, smaller cavity heights,relatively low-values of optical attenuation, and/or other features withthe cables of the present invention. Of course, bend resistant opticalfibers may be used in other cable embodiments such as embodiments havingless than four ribbons in the stack or with round cables. FIG. 18 cdepicts cable 180″ that is similar to cable 180, but includes aplurality of ribbons 182″ having bend resistant optical fibers 312. Morespecifically, cable 180″ includes six ribbons 182″ having a suitablenumber of bend resistant optical fibers (e.g., 12-f, 24-f, 36-f, of 48-fribbons) for the desired fiber count in the cable. Bend resistantoptical fibers such as bend resistant optical fiber 312 is described inmore detail herein. Additionally, the disclosure discusses where the useof bend resistant optical fibers allows improved performance and/orchanges to the design parameters of cable 180″ and/or other similarcables.

Ribbon 182 includes twenty-four optical fibers and is a portion of aribbon stack (not numbered) formed by the plurality of ribbons 182 thatare at least partially disposed within cavity 188 a (FIG. 18 c) of cablejacket 188. Ribbons of the stack may employ a splittable constructionusing subunits and/or stress concentrations as known in the art, therebyallowing separation of the ribbon into smaller groups of optical fibers.Of course, ribbons could use any suitable number of optical fibersand/or different ribbons could have different numbers of optical fibers.A first dry insert 184 a and a second dry insert 184 b are disposedwithin the cavity and are generally disposed on opposite sides of theribbon stack (or optical fibers as in cable 180′). As depicted in cable180, dry inserts 184 a, 184 b are generally aligned with a major surface(i.e. the horizontal side) of cavity 188 a at the top and bottom andalso generally aligned with the width (i.e. major surfaces) of theribbons, thereby forming an optical ribbon/dry insert composite stackwithin cavity 188 a. Consequently, the rectangular (or square) ribbonstack is fitted to a corresponding generally rectangular (or square)cavity and avoids the issues associated with placing a rectangular (orsquare) ribbon stack within a round buffer tube (i.e. stresses on thecorner fibers of the ribbon stack in a round buffer tube that may causethe cable to fail optical performance requirements such as occursbending). Dry inserts 184 a, 184 b act to couple, cushion, and allowmovement and separation of the ribbons (or optical fibers) toaccommodate bending of cable 180. Moreover, one or more of the dryinserts may optionally provide water-blocking.

Fiber optic cables like cable 180 are advantageous as distributioncables since they can have a relatively high optical waveguide countwith a relatively small cross-sectional footprint. By way of example,one explanatory embodiment of cable 180 has four ribbons with eachribbon having twenty-four optical fibers for a total fiber count ofninety-six fibers. Additionally, the four ribbons of this explanatoryembodiment have an excess ribbon length (ERL) of about 0.5% or more suchas in range of about 0.6% to about 0.8%, but other embodiments may haveother values of ERL. With twenty-four fiber ribbons, cable 180 has amajor cable dimension W of about 15 millimeters or less and a minorcable dimension H of about 8 millimeters or less. Furthermore, strengthmembers 189 of this explanatory embodiment are formed from aglass-reinforced plastic (GRP) and have a dimension D of about 2.3millimeters, which is smaller than the height of cavity 188 a. Theminimum bend radius of this explanatory embodiment is about 125millimeters which allows the cable to be coiled in a relatively smalldiameter for slack storage.

Of course, other suitable fiber/ribbon counts, components, ERL and/orcable dimensions are possible with the concepts of the invention.Illustratively, cables similar to cable 180 could have four ribbons withdifferent fiber counts such as: (1) twelve fiber ribbons with a majorcable dimension W of about 12 millimeters or less for a total offorty-eight optical fibers; (2) thirty-six fiber ribbons with a majorcable dimension W of about 18 millimeters or less for a total ofone-hundred and forty-four optical fibers; or (3) forty-eight fiberribbons with a major cable dimension W of about 25 millimeters or lessfor a total of two-hundred and sixteen optical fibers. Furthermore,cables using bend resistant optical fibers can have higher ribbon and/oroptical fiber counts. For instance, cable 180″ can have a relativelyhigh-fiber count by using six 48-f ribbons for a total of 288-f in thecable. On the other hand, a cable similar to cable 180″ can have arelatively low-fiber count by using five 12-f ribbons for a total of60-f in the cable. Additionally, cables using bend resistant opticalfibers may reduce the stiffness of the same and/or approach the designedge for the long-term bend strength of the strength members such as byusing smaller strength members. By way of example, cable 180 may reducethe diameter of the strength members to about 2.0 millimeters, therebyreducing the stiffness of the cable to allow smaller bend radii and/orcoil diameters for the same.

FIG. 18 c schematically depicts cavity 188 a of a cable such as cable180 or other similar cable. Cavity 188 a has a cavity height CH and acavity width CW. By way of example for explanatory embodiment discussedabove, each ribbon 182 has a height of about 0.3 millimeters for a fiber(ribbon) height FH of about 1.2 millimeters (4 times 0.3 millimeters)and cavity 188 a has a cavity height CH of about 5 millimeters such asabout 5.2 millimeters. Cavity width CW is generally determined by thewidth of the ribbons (or number of optical fibers) intended for thecable and would be about 7-8 millimeters such as about 8.1 millimetersfor the twenty-four fiber ribbons. Dry inserts 184 a, 184 b occupy thecavity on the top and bottom of the ribbon stack. In one embodiment, dryinserts 184 a, 184 b have an uncompressed height h of about 1.8millimeters, but other suitable uncompressed heights h for dry insertsare possible. As depicted by bar 39 in FIG. 3, this explanatoryembodiment with a 5.5 millimeter cavity height CH, fiber height FH ofabout 1.2 millimeters, and two 1.8 millimeter dry inserts had anormalized ribbon pullout force of about 1.5 N/m, but other suitablenormalized ribbon pullout forces are possible. The compression of thedry inserts 184 a, 184 b is the localized maximum compression of the dryinsert and generally occurs where the ribbon or ribbon stack has themaximum displacement from the neutral axis if the cable includes apositive ERL as schematically depicted in FIG. 19 a.

Illustratively, the explanatory embodiment has a total height for theuncompressed dry inserts and the fiber (i.e. ribbon) height FH of about4.8 millimeters, which is less than the cavity height of 5.2millimeters. Consequently, the normalized ribbon pullout force isgenerally caused by the undulating ribbon stack causing localizedmaximum compression due to the ERL and/or friction. By way of example,proper coupling of the ribbon stack (or ribbons or optical fibers) tothe cable jacket may be achieved when the combined uncompressed heightof the dry inserts is about 40% or more of the cavity height CH such asby using two 1 millimeter dry inserts with a cavity having a cavityheight CH of about 5 millimeters. Of course, other suitable ratios arepossible as long as optical performance is preserved. In the explanatoryembodiment, the combined uncompressed height (2 times 1.8 millimetersequals 3.6 millimeters) of the dry inserts is about 69% of the cavityheight CH (5.2 millimeters), which is more than 50% of the cavity heightCH. It is also possible to specify the ratio of fiber height FH (i.e.,ribbon stack height) to cavity height CH. The ratio of fiber height FHto cavity height CH is generally about 25% or more, but could have othervalues. By way of example, four ribbons having a fiber height FH of 1.2millimeters are disposed within the cavity height CH of about 4.8millimeters, but the cavity height CH could be smaller which increasesthe ratio of fiber height FH to cavity height CH. For instance, asmaller cavity height CH of about 3.4 millimeters gives a ratio of about35% for the four ribbons having a fiber height FH of 1.2 millimeters.The space not occupied by the ribbons allows the ribbons to have ERLwithin the cable.

Of course, the cavity, ribbons, and/or dry inserts can have othersuitable dimensions while still providing suitable performance. Forinstance, thinner ribbons and/or dry inserts may be used.Illustratively, optical fibers with smaller coated outer diameters suchas 125 microns; instead of 250 microns, may be used in ribbons forreducing the ribbon height. Consequently, the ribbons have a smallerheight of about 0.15 millimeters, thereby allowing twice as many ribbonswith the same fiber height FH as ribbons with a height of 0.30millimeters. Additionally, using smaller diameter optical fibers allowsmore fibers for a given ribbon width so that the cable designs such as576-fibers or more are possible with a relatively small cross-sectionfootprint (i.e., the number of optical fibers double; however the cablecross-section remains about the same size as the cables having 250micron fibers). Although cavity 188 a is depicted as rectangular it maybe difficult to make a cavity with a rectangular cross-section as shown,i.e., the extrusion process may create the cavity with a somewhatirregular rectangular shape. Likewise, the cavity can have othersuitable shapes besides generally rectangular such as oval, round or thelike, which may generally change the relationship (alignment) among thedry insert, ribbon, and/or cavity. Furthermore, the cable jacket canhave other variations such as concave upper and lower walls forimproving side crush performance of the cables, which slightly modifiescross-section of the cavity.

Dry inserts 184 a, 184 b may be any suitable material such as acompressible layer of, for instance, foam tape for cushioning, coupling,allowing movement of and accommodating bending of the ribbon(s) (oroptical fiber(s)) within cavity 188 a or other suitable materials. Asdepicted, dry inserts 184 a, 184 b may optionally also include awater-swellable layer for blocking the migration of water along cavity188 a. By way of example, the dry insert may include a water-swellabletape that is laminated to a compressible layer such as an open-cellpolyurethane foam tape, but of course other suitable materials andconstruction are possible for dry insert(s). Likewise, cables of thepresent invention may have a dry insert and a separate water blockingcomponent such as a water-swellable yarn or thread disposed within thecavity. In other words, the dry insert and water blocking component maybe separate components. As depicted, the water-swellable layer of dryinserts 184 a, 184 b generally faces the cavity wall (i.e., is separatedfrom the optical fibers or ribbons), but in other embodiments thewater-swellable layer may face the optical fiber(s) or ribbons. In afurther cable variation, water-swellable tapes are generally alignedwith the ribbons in a sandwich configuration in the cavity like in cable180; however, this cable variation may not provide the desired ribboncoupling.

Generally speaking, positioning dry inserts on opposite ends of theribbon stack (or single ribbon or loose optical fibers) aids ininfluencing and maintaining a generally uniform ERL distribution alongthe cable during different conditions, thereby helping to preserveoptical performance. FIGS. 19 and 19 a are schematic representationsrespectively showing the ribbon stacks of two different cables 192,192a, that are similar to cable 180, laid out in a straight configuration(i.e. not in a bending condition). A neutral axis NA of cables 192,192 ais represented by the dashed line. More specifically, FIG. 19 representscable 192 with a ribbon stack 194 having zero ERL and FIG. 19 arepresents cable 192 a with a ribbon stack 194 a having a positive ERL.As shown, ribbon stack 194 (no ERL) is generally straight within cable192 along the neutral axis NA and ribbon stack 194 a (positive ERL) hasa generally undulating profile about the neutral axis NA to accommodatethe ERL. When cables 192,192 a are bent the ribbons reposition withinthe cable to accommodate length changes in the cavity due to bending(i.e. the upper surface of the cavity lengthens and the bottom surfaceof the cavity is shorter).

FIGS. 19 b and 19 c are schematic representations respectively showingcables 192,192 a during bending with the two middle ribbons removed forclarity. As depicted in FIG. 19 b, a top ribbon RT of ribbon stack 194(having no ERL) generally moves to a low-stress state near the neutralaxis NA of the cable during bending. Consequently, top ribbon RT pushesdown on the other ribbons of ribbon stack 194, thereby causing severebending on the bottom ribbon (along with the other ribbons) of the stackthat may cause relatively high levels of optical attenuation or evendark optical fibers. As shown, top ribbon RT forces a bottom ribbon BRof ribbon stack 194 (with no ERL) into sharp bends (see the arrows) thatcause relatively high levels of attenuation. On the other hand, FIG. 19c shows that ribbon stack 194 a (positive ERL) allows the top ribbon togenerally remain above the neutral axis NA of cable 192 a, therebyallowing bottom ribbon BR to have a more gradual bends (i.e. the bend isgenerally sinusoidal), thereby preserving optical performance of bottomribbon RB. Moreover, ribbon to cable coupling is beneficial forinfluencing a relatively even ERL distribution along the cable such asduring bending, which generally allows for small cable bend radii. Otherfactors such as the size of cavity and/or compression of the dryinsert(s) may also influence ERL/EFL distribution along the cable.

Another optical performance aspect of cables having a generally flatprofile with a non-stranded ribbon stack is the total amount of ERLrequired for suitable cable performance. The amount of ERL for adequatecable performance generally depends on the cable design such as thenumber of ribbons and/or type of optical fiber used. Generally speaking,the minimum ERL for cables having a single ribbon is determined by thedesired allowable level of fiber strain at the rated cable load;whereas, the minimum ERL for a multiple ribbon cable is generallyinfluenced by bending performance. More specifically, when selecting theminimum ERL limit for a cable design the strength member geometry andmaterial (i.e. cross-sectional area and Young's modulus) should beconsidered for calculating the desired level of fiber strain at therated tensile load of the cable design. Additionally, the amount of ERLrequired for bending generally increases as the number of ribbons in thestack increases since the outer ribbons of the ribbon stack are fartherfrom the neutral axis of the cable. However, there are limits on theupper end of ERL for suitable optical performance (i.e. too much ERL candegrade optical performance). A near optimal upper level of ERL can becalculated using the cavity height CH, ribbon thickness t_(r), and thedesired minimum bend radius R. Equation 1 is a formula for generallymatching the bend of the upper surface of the cavity with bend in theribbon to determine a near optimal upper level of ERL. However, cablescan use an upper level for ERL that is greater than given by the formulaand still have suitable cable performance. The use of bend resistantoptical fibers also may allow elevated levels of ERL.

$\begin{matrix}{{{Upper}\mspace{14mu}{Level}\mspace{14mu}{ERL}} = {50\left( \frac{h - t_{r}}{R} \right)}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$As an example of Equation 1, a cable having a cavity height CH of about4 millimeters, a ribbon thickness of about 0.3 millimeters, and adesired minimum bend radius of about 150 millimeters would have a nearoptimal upper level of ERL of about 1.2%. Furthermore, cables havingrelatively high levels of ERL such as in the range of 0.6% to 1.5% maybe suitable for self-supporting installations such as NESC heavyloading, but the particular ERL for a given design should have thedesired cable performance. Furthermore, cables having bend resistantoptical fibers may have even higher levels of ERL such as 1.5% orgreater such as up to 2.0% or more. On the other hand, cables such ascable 180′ having loose optical fibers 12 may have lower values ofexcess fiber length (EFL) such as about 0.2% EFL since all the opticalfibers are located near the neutral axis of the cable.

Although, dry inserts 184 a, 184 b of cable 180 are disposed on both thetop and bottom of the ribbon stack, one or more dry inserts may bewrapped about the optical fibers or disposed on one or more sidesthereof as depicted in FIG. 20. Specifically, FIG. 20 shows fourindependent dry inserts 204 a, 204 b, 204 c, 204 d disposed about theribbon stack. In another other embodiment, two dry inserts may be placedon the sides of the ribbon stack (i.e. the locations of dry inserts 204c, 204 d) instead of the top and bottom of the ribbon stack. In stillanother embodiment, cables of the present invention can include a singledry insert such as on one side of the ribbon stack or in the middle ofthe stack (i.e. ribbons on both sides of the dry insert). Othervariations include side-by-side ribbons stacks and/or including a markersuch as using paper, mylar, or the like between ribbons or ribbon stacksfor identification and/or separation of the ribbons in the cable.

FIG. 21 depicts cable 210 that is similar to cable 180, but it furtherincludes at least one armor layer 211 and in this embodiment two armorlayers 211. Armor layers 211 are respectively positioned above and belowthe cavity for inhibiting unintended breaches such as from rodents orpoint crushing contacts. Armor layer 211 can be formed from any suitablematerial such as a conductive material such as steel or a dielectricsuch as polyamide, polycarbonate, or a braided fabric formed fromfiberglass, aramid or the like. FIG. 22 depicts another cable 220 thatincludes at least one armor layer 221. Cable 220 is similar to cable180, but has armor layer 221 wrapped about a cable jacket 228 and isfurther upjacketed with a second jacket 228 a, thereby covering armorlayer 221.

FIG. 23 depicts cable 230 that is similar to cable 180, but it furtherincludes a tube 231 for protecting the optical fibers. Tube 231 can beformed from any suitable material and further protects the opticalfibers of the cable. Tube 231 may be formed in a separate extrusionprocess or as a co-extrusion with a cable jacket 238. Tube 231, alongwith cable jackets, may be formed from any suitable material such as apolymer. By way of example, one embodiment has a tube formed of HDPE andcable jacket is formed from a MDPE, but any suitable combination ofmaterials may be used. Likewise, flame retardant materials may be used,thereby making the cables suitable for indoor applications.Additionally, cable 230 further includes a toning lobe 238 a having atoning wire 233 useful for locating the cable in buried applications.Toning lobe 238 a is connected to cable jacket 238 by a web (notnumbered), thereby allowing toning lobe 238 a to be separated from themain cable body. Additionally, cables without a toning lobe may have thecapability of being tonable by using one or more cable components thatare conductive. Furthermore, cables can conduct electrical power if oneor more of the cable components are conductive such as including atwisted pair of copper wires or using conductive strength members.

FIGS. 24 and 25 respectively depict cables 240 and 250 that are similarto cable 180, but have different cross-sectional cable shapes. Cable 240depicts a generally dogbone cable cross-section for cable jacket 248 andcable 250 illustrates another variation on the cable cross-section.Cable 250 has recessed portions 258 a so that the craft can separate oneor more of strength members 259 along a portion of the cable. Of course,other cross-sectional shapes are possible with the concepts of theinvention.

FIG. 26 schematically illustrates an exemplary one-pass manufacturingline 260 for cable 180 according to the present invention; however,other variations of the concepts may be used to manufacture otherassemblies and/or cables according to the concepts of the presentinvention. One pass manufacturing line 260 includes at least one opticalribbon payoff reel 261, a plurality of dry insert payoff reels 262, aplurality of strength member payoff reels 263, a plurality of strengthmember capstans 264, a cross-head extruder 265, a water trough 266, oneor more caterpullers 267, and a take-up reel 269. Additionally, cable180 may further include an armor layer and a second cable jackettherearound, thereby forming a cable similar to cable 220 as illustratedin FIG. 22. The armor layer and/or second cable jacket can bemanufactured on the same line as cable 180 or on a second manufacturingline. The exemplary manufacturing process includes paying-off at leastone optical fiber ribbon 182 and dry insert 184 a, 184 b from respectivereels 261, 262, and 262. Only one payoff reel for optical fiber ribbon182 is shown for clarity. However, manufacturing lines can include anysuitable number of payoff reels for one or more ribbons or opticalfibers in order to manufacture assemblies and/or cables according to thepresent invention. Thereafter, dry inserts 184 a, 184 b are generallypositioned about optical fiber ribbon 182, thereby forming cable core185 (i.e. a dry insert-ribbon composite stack or sandwich).Additionally, strength members 189 are paying-off respective reels 263under a relatively high tension (e.g. between about 100 to about 400pounds) using respective strength member capstans 264, therebyelastically stretching strength members 189 (represented by the arrows)so that ERL is produced in the cable. In other words, after the tensionis released on strength members 189 they return to their originalunstressed length (i.e. shorten), thereby producing ERL since theribbons were introduced into the cable with about the same length astensioned strength members and the ribbons were not stretched. Statedanother way, the amount of ERL produced is equal to about the strengthmember strain (i.e., elastically stretching of the strength member) plusany plastic shrinkage of the cable jacket that may occur. The strengthmember strain can create a significant amount of ERL or EFL in aone-pass production such as 10% or more, 25% or more, 50% or more, andeven up to 80% or more of the total ERL or EFL within the cable.Furthermore, elastically stretching of the strength member isadvantageous since it allows for a precise control of the amount of ERLor EFL being introduced into the cable and greatly reduces strengthmember pistoning since the finished cable jacket is in compressioninstead of tension. For the manufacture of cable 180, about 95% of ERLis introduced into the cable by elastically stretching the strengthmembers. Thereafter, cable core 185 and strength members 189 are fedinto cross-head extruder 265 where cable jacket 188 is extruded aboutcable core 185 and strength members 189, thereby forming cable 180. Asshown by FIG. 26, cable jacket is being applied about the at least oneoptical fiber and at least one strength member by cross-head extruder265 while the strength member is elastically stretched. After extrusion,cable 180 is then quenched in water trough 266 while the strength memberis still elastically stretched, thereby allowing the cable jacket to“freeze” on the stretched strength members. Cable 180 is pulled throughthe manufacturing line using one or more caterpullers 267 and then woundonto take-up reel 269 under low tension (i.e., the tensile force thatelastically stretched the strength members is released and strengthmembers return to a relaxed length thereby creating ERL or EFL in thecable). As depicted in the box, if one manufacturing line is set-up tomake cable similar to cable 220, then a second caterpuller 267 is usedfor pulling the cable assembly as the armor layer 221 is paid-off a reel270 and formed about cable 180 using suitable armor forming equipment(not depicted), and a second jacket 188 a is extruded thereover using across-head extruder 272. Thereafter, the armored cable 180′ passes intoa second water trough 274 before being wound-up on take-up reel 269.Additionally, other cables and/or manufacturing lines according to theconcepts of the present invention are possible. For instance, cablesand/or manufacturing lines may include a water-swellable tape, yarn, orthe like; however, the use of one or more other suitable cablecomponents is possible.

The cables of the present invention may also advantageously use opticalfibers that are relatively bend resistant for preserving opticalperformance when subjected to relatively small bend radii. For instance,cable 180″ has relatively small delta attenuation when coiled into arelatively small bend radius. By way of example, when bent into a coilhaving a single turn with a diameter of about 400 millimeters (i.e., aradius of about 100 millimeters) optical fiber 312 of fiber optic cablehas a delta optical attenuation of about 0.1 dB or less per turn, andmore preferably about 0.03 dB or less per turn, thereby preservingsuitable levels of optical performance for the fiber optic cable. Forinstance, slack storage of several turns such as 3 or more turns ofcable 180″ into a coil having a diameter of about 200 millimeters wouldresult in the delta optical attenuation of about 0.4 dB or less.

By way of example, bend resistant optical fibers may havemicrostructures and/or other configurations that allow reduced bendradii while preserving optical performance. Microstructured opticalfibers disclosed herein comprise a core region and a cladding regionsurrounding the core region, the cladding region comprising an annularhole-containing region comprised of non-periodically disposed holes suchthat the optical fiber is capable of single mode transmission at one ormore wavelengths in one or more operating wavelength ranges. The coreregion and cladding region provide improved bend resistant, and singlemode operation at wavelengths preferably greater than or equal to 1500nm, in some embodiments also greater than 1400 nm, in other embodimentsalso greater than 1260 nm. The optical fibers provide a mode field at awavelength of 1310 nm preferably greater than 8.0 microns, morepreferably between 8.0 and 10.0 microns. In preferred embodiments,optical fiber disclosed herein is thus single-mode transmission opticalfiber.

In some embodiments, the microstructured optical fiber disclosed hereincomprises a core region disposed about a longitudinal centerline, and acladding region surrounding the core region, the cladding regioncomprising an annular hole-containing region comprised ofnon-periodically disposed holes, wherein the annular hole-containingregion has a maximum radial width of less than 12 microns, the annularhole-containing region has a regional void area percent of less than 30percent, and the non-periodically disposed holes have a mean diameter ofless than 1550 nm.

By “non-periodically disposed” or “non-periodic distribution”, we meanthat when one takes a cross section (such as a cross sectionperpendicular to the longitudinal axis) of the optical fiber, thenon-periodically disposed holes are randomly or non-periodicallydistributed across a portion of the fiber. Similar cross sections takenat different points along the length of the fiber will reveal differentcross-sectional hole patterns, i.e., various cross sections will havedifferent hole patterns, wherein the distributions of holes and sizes ofholes do not match. That is, the voids or holes are non-periodic, i.e.,they are not periodically disposed within the fiber structure. Theseholes are stretched (elongated) along the length (i.e. in a directiongenerally parallel to the longitudinal axis) of the optical fiber, butdo not extend the entire length of the entire fiber for typical lengthsof transmission fiber.

For a variety of applications, it is desirable for the holes to beformed such that greater than 95% of and preferably all of the holesexhibit a mean hole size in the cladding for the optical fiber which isless than 1550 nm, more preferably less than 775 nm, most preferablyless than about 390 nm. Likewise, it is preferable that the maximumdiameter of the holes in the fiber be less than 7000 nm, more preferablyless than 2000 nm, and even more preferably less than 1550 nm, and mostpreferably less than 775 nm. In some embodiments, the fibers disclosedherein have fewer than 5000 holes, in some embodiments also fewer than1000 holes, and in other embodiments the total number of holes is fewerthan 500 holes in a given optical fiber perpendicular cross-section. Ofcourse, the most preferred fibers will exhibit combinations of thesecharacteristics. Thus, for example, one particularly preferredembodiment of optical fiber would exhibit fewer than 200 holes in theoptical fiber, the holes having a maximum diameter less than 1550 nm anda mean diameter less than 775 nm, although useful and bend resistantoptical fibers can be achieved using larger and greater numbers ofholes. The hole number, mean diameter, max diameter, and total void areapercent of holes can all be calculated with the help of a scanningelectron microscope at a magnification of about 800× and image analysissoftware, such as ImagePro, which is available from Media Cybernetics,Inc. of Silver Spring, Md., USA.

The optical fiber disclosed herein may or may not include germania orfluorine to also adjust the refractive index of the core and or claddingof the optical fiber, but these dopants can also be avoided in theintermediate annular region and instead, the holes (in combination withany gas or gases that may be disposed within the holes) can be used toadjust the manner in which light is guided down the core of the fiber.The hole-containing region may consist of undoped (pure) silica, therebycompletely avoiding the use of any dopants in the hole-containingregion, to achieve a decreased refractive index, or the hole-containingregion may comprise doped silica, e.g. fluorine-doped silica having aplurality of holes.

In one set of embodiments, the core region includes doped silica toprovide a positive refractive index relative to pure silica, e.g.,germania doped silica. The core region is preferably hole-free. Asillustrated in FIG. 27, in some embodiments, the core region 370comprises a single core segment having a positive maximum refractiveindex relative to pure silica Δ₁ in %, and the single core segmentextends from the centerline to a radius R₁. In one set of embodiments,0.30%<Δ₁<0.40%, and 3.0 μm<R₁<5.0μm. In some embodiments, the singlecore segment has a refractive index profile with an alpha shape, wherealpha is 6 or more, and in some embodiments alpha is 8 or more. In someembodiments, the inner annular hole-free region 382 extends from thecore region to a radius R₂, wherein the inner annular hole-free regionhas a radial width W12, equal to R2-R1, and W12 is greater than 1 μm.Radius R2 is preferably greater than 5 μm, more preferably greater than6 μm. The intermediate annular hole-containing region 384 extendsradially outward from R2 to radius R3 and has a radial width W23, equalto R3-R2. The outer annular region 386 extends radially outward from R3to radius R4. Radius R4 is the outermost radius of the silica portion ofthe optical fiber. One or more coatings may be applied to the externalsurface of the silica portion of the optical fiber, starting at R4, theoutermost diameter or outermost periphery of the glass part of thefiber. The core region 370 and the cladding region 380 are preferablycomprised of silica. The core region 370 is preferably silica doped withone or more dopants. Preferably, the core region 370 is hole-free. Thehole-containing region 384 has an inner radius R2 which is not more than20 μm. In some embodiments, R2 is not less than 10 μm and not greaterthan 20 μm. In other embodiments, R2 is not less than 10 μm and notgreater than 18 μm. In other embodiments, R2 is not less than 10 μm andnot greater than 14 μm. The hole-containing region 384 has a radialwidth W23 which is not less than 0.5 μm. In some embodiments, W23 is notless than 0.5 μm and not greater than 20 μm. In other embodiments, W23is not less than 2 μm and not greater than 12 μm. In other embodiments,W23 is not less than 2 μm and not greater than 10 μm. Such fiber can bemade to exhibit a fiber cutoff of less than 1400 nm, more preferablyless than 1310 nm, and a 20 mm macrobend induced loss of less than 1dB/turn, preferably less than 0.5 dB/turn, even more preferably lessthan 0.1 dB/turn, still more preferably less than 0.05 dB/turn, yet morepreferably less than 0.03 dB/turn, and even still more preferably lessthan 0.02 dB/turn, and more preferably a 12 mm macrobend induced loss ofless than 5 dB/turn, preferably less than 1 dB/turn, and more preferablyless than 0.5 dB/turn, and a 8 mm macrobend induced loss of less than 5dB/turn, preferably less than 1 dB/turn, more preferably less than 0.5dB/turn with the macrobend induced loss being measured at a referencewavelength of 1550 nanometers.

An example of a suitable bend resistant optical fiber 312 is illustratedin FIG. 28. Optical fiber 312 in FIG. 28 comprises a core region whichis surrounded by a cladding region which comprises randomly disposedvoids which are contained within an annular region spaced from the coreand positioned to be effective to guide light along the core region.Additionally, other types of bend resistant optical fibers may be usedwith the concepts of the present invention.

Many modifications and other embodiments of the present invention,within the scope of the appended claims, will become apparent to askilled artisan. For example, optical waveguides can be formed in avariety of ribbon stacks or configurations such as a stepped profile ofthe ribbon stack (i.e. the ribbon stack cross-section is in the shape ofa plus sign). Cables according to the present invention can also includemore than one optical tube assembly stranded helically, rather than S-Zstranded configurations. Additionally, dry inserts of the presentinvention can be laminated together as shown or applied as individualcomponents. Therefore, it is to be understood that the invention is notlimited to the specific embodiments disclosed herein and thatmodifications and other embodiments may be made within the scope of theappended claims. Although specific terms are employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation. The invention has been described with reference tosilica-based optical waveguides, but the inventive concepts of thepresent invention are applicable to other suitable optical waveguidesand/or cable configurations.

1. A fiber optic cable comprising: a plurality of fiber optic ribbons,the plurality of fiber optic ribbons having an excess ribbon lengthgreater than 1.2%; a cable jacket having a cavity, wherein the pluralityof fiber optic ribbons are at least partially disposed within thecavity; at least one dry insert having a water-swellable element andincluding a foam tape, the at least one dry insert being disposed withinthe cavity and contacting at least one of the plurality of fiber opticribbons for coupling the plurality of fiber optic ribbons to the cablejacket; and at least two strength members that are disposed on oppositesides of the cavity.
 2. The fiber optic cable of claim 1, the ERL beingabout 1.5% or greater.
 3. The fiber optic cable of claim 1, wherein atleast one of the optical fiber ribbons has a plurality of bend resistantoptical fibers.
 4. The fiber optic cable of claim 1, wherein the atleast one dry insert comprises a first dry insert and a second dryinsert having a combined uncompressed height, the combined uncompressedheight being about 40% or more of a cavity height of the cavity.
 5. Thefiber optic cable of claim 1, wherein each optical fiber ribboncomprises twenty-four or more optical fibers and the plurality of fiberoptic ribbons comprises four or more optical fiber ribbons.
 6. The fiberoptic cable of claim 1, wherein the ribbons are arranged in a stackhaving a fiber height that is about 25% or more of a cavity height. 7.The fiber optic cable of claim 1, wherein the at least one dry insertcomprises a compressible layer.
 8. The fiber optic cable of claim 1,wherein the water-swellable element is a water-swellable layer facingoutward towards a wall of the cavity.
 9. The fiber optic cable of claim1, wherein the at least one dry insert includes a plurality ofmicrospheres.
 10. The fiber optic cable of claim 1, wherein the at leastone dry insert comprises a matrix material and a plurality of filaments.11. The fiber optic cable of claim 1, wherein each strength member has astrength member diameter, wherein the cavity has a cavity height and thecavity height is larger than the strength member diameter.
 12. The fiberoptic cable of claim 1, a minor dimension of the fiber optic cable beingabout 15 millimeters or less and a major dimension of the fiber opticcable being about 25 millimeters or less.
 13. The fiber optic cable ofclaim 1, further comprising a component having a water-swellablecharacteristic or a water-blocking characteristic.
 14. The fiber opticcable of claim 1, wherein the plurality of optical fiber ribbons arenon-stranded within the cavity.
 15. The fiber optic cable of claim 1,wherein the cavity has a generally rectangular shape.
 16. A fiber opticcable comprising: a plurality of fiber optic ribbons, the plurality offiber optic ribbons having an excess ribbon length greater than 1.2%; acable jacket having a cavity, wherein the plurality of fiber opticribbons are at least partially disposed within the cavity; at least onedry insert having a water-swellable element, the at least one dry insertbeing disposed within the cavity and contacting at least one of theplurality of fiber optic ribbons for coupling the plurality of fiberoptic ribbons to the cable jacket; and at least two strength membersthat are disposed on opposite sides of the cavity, wherein the at leastone dry insert includes a felt substance.
 17. A fiber optic cablecomprising: a plurality of fiber optic ribbons, the plurality of fiberoptic ribbons having an excess ribbon length greater than 1.2%; a cablejacket having a cavity, wherein the plurality of fiber optic ribbons areat least partially disposed within the cavity; at least one dry inserthaving a water-swellable element, the at least one dry insert beingdisposed within the cavity and contacting at least one of the pluralityof fiber optic ribbons for coupling the plurality of fiber optic ribbonsto the cable jacket; and at least two strength members that are disposedon opposite sides of the cavity, wherein the at least one dry insertcomprises a first dry insert and a second dry insert, and wherein theplurality of optical fiber ribbons are disposed between the first dryinsert and the second dry insert and the first dry insert and the seconddry insert contact the jacket.
 18. A fiber optic cable comprising: aplurality of fiber optic ribbons, the plurality of fiber optic ribbonshaving an excess ribbon length greater than 1.2%; a cable jacket havinga cavity, wherein the plurality of fiber optic ribbons are at leastpartially disposed within the cavity; at least one dry insert having awater-swellable element, the at least one dry insert being disposedwithin and contacting the cavity and contacting at least one of theplurality of fiber optic ribbons for coupling the plurality of fiberoptic ribbons to the cable jacket, wherein the at least one dry inserthas a combined uncompressed height, the combined uncompressed heightbeing about 40% or more of a cavity height of the cavity; and at leasttwo strength members, the strength members being disposed on oppositesides of the cavity and contacting the cable jacket.
 19. The fiber opticcable of claim 18, wherein each strength member has a strength memberdiameter, wherein the cavity has a cavity height and the cavity heightis larger than the strength member diameter.
 20. The fiber optic cableof claim 19, wherein the cavity has a generally rectangular shape. 21.The fiber optic cable of claim 19, a minor dimension of the fiber opticcable being about 15 millimeters or less and a major dimension of thefiber optic cable being about 25 millimeters or less.
 22. The fiberoptic cable of claim 18, the at least one dry insert comprising a firstdry insert and a second dry insert having together the a combineduncompressed height, wherein the plurality of fiber optic ribbons aredisposed between the first and second dry inserts.
 23. A fiber opticcable comprising: a plurality of fiber optic ribbons, the plurality offiber optic ribbons having an excess ribbon length greater than 1.2%; acable jacket having a generally rectangular cavity, wherein theplurality of fiber optic ribbons are at least partially disposed withinthe cavity; a first compressible foam dry insert; a second dry insert,the first and second dry inserts having a combined uncompressed heightand coupling the plurality of fiber optic ribbons to the cable jacket,the combined uncompressed height being about 40% or more of a cavityheight of the cavity; and at least two strength members, the strengthmembers being disposed on opposite sides of the cavity and contactingthe cable jacket.
 24. The fiber optic cable of claim 23, wherein eachstrength member has a strength member diameter, wherein the cavity has acavity height and the cavity height is larger than the strength memberdiameter.
 25. The fiber optic cable of claim 23, a minor dimension ofthe fiber optic cable being about 15 millimeters or less and a majordimension of the fiber optic cable being about 25 millimeters or less.